This application claims the benefit of Korean Application No. 2000-72939 filed Dec. 4, 2000, in the Korean Patent Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a recording medium including a header region on which header information is recorded, and a method of and an apparatus for detecting the header region, and more particularly, to a recording medium including a wobbled track on which user data is recorded and a header region on which header information is recorded, and a method of and an apparatus for detecting the header region.
2. Description of the Related Art
A groove is formed along each track on an optical disc such as a digital versatile disc-random access memory (DVD-RAM) to allow a recording laser beam to exactly follow the track. Land corresponding to the surface of a substrate exists between grooves. Data is recorded on a groove track and/or a land track. A track is divided into a plurality of sectors and managed.
A wobble signal of a specified frequency is recorded on a groove track and/or a land track on an optical disc through a change in direction of an amplitude. The wobble signal is used for recording an auxiliary clock signal for obtaining synchronizing information during recording or reproduction. In other words, the wobble signal has a frequency band which does not influence a tracking servo mechanism provided in a recording/reproducing apparatus and is used as an auxiliary signal supplementing a system clock. According to DVD-RAM specifications, a servo band for tracking in a radial direction is about 10 KHz, and the frequency of the wobble signal is about 157 KHz at a standard linear velocity.
A header region is disposed on a track to record header information of each sector thereon. According to the DVD-RAM specifications, the header region is formed of pre-pits when a substrate is manufactured. The header region comprises a variable frequency oscillator (VFO) region for phase locked loop (PLL), a physical identification data (PID) region assigned a sector number and an identification (ID) error detection (IED) region which stores ID error detection information. A header region is disposed at a predetermined portion of a sector. A pickup device provided in a recording/reproducing apparatus searches for and moves to a desired position based on information recorded on a header region. The pickup device recognizes a sector number, a sector type and a land track or a groove track and performs servo control, using the information recorded on the header region.
FIG. 1 is a schematic diagram illustrating a conventional wobbled track. Referring to FIG. 1, on an optical disc having a conventional wobbled track, a header region on which header information is recorded is provided at a boundary between a sector N-1 and a sector N. According to the DVD-RAM specifications, the two portions of the header region are displaced from a track center to the right and to the left, respectively, by a xc2xd track at the beginning of the sector N.
FIGS. 2A-2D are diagrams for explaining a method of detecting the header region of FIG. 1. Referring to FIG. 2A, in a channel 2 signal detected through a channel 2, a wobble signal having a specified frequency constantly appears in a wobbled region. However, a rapid signal change occurs in the header region because a high frequency signal for header information is recorded on the header region. Accordingly, as shown in FIG. 2A, the channel 2 signal is amplified and then low-pass filtered. Thereafter, the channel 2 signal is sliced on the basis of a predetermined reference slice level, thereby obtaining an upper sliced signal and a lower sliced signal as shown in FIGS. 2B and 2C, respectively. An OR operation is performed on the upper sliced signal and the lower sliced signal, thereby obtaining a header detection signal as shown in FIG. 2D. A region corresponding to a portion of a high level in the header detection signal is the header region.
Reliable detection of a header region is essential to control of rotation of an optical disc and is necessarily required to exactly read various information recorded on a header region. This is particularly essential to an optical disc as a recording medium with a high precision. However, as described in FIG. 1, the header region is continuously disposed between the sector N-1 and the sector N so that it becomes a gap in a wobble signal. Such a gap affects detection of the channel 2 signal as external disturbance, so that it is difficult to exactly detect the start position of the header region.
To solve the above problem, it is an object of the present invention to provide a recording medium with a wobbled track, from which a header region may be more reliably detected, and a method of and an apparatus for detecting the header region.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and, in part, will be obvious from the description, or may be learned by practice of the invention.
Accordingly, to achieve the above and other objects of the invention, one aspect of the invention provides a recording medium comprising a wobbled track on which a wobble signal is recorded, a header region on which header information is recorded, and a wobble-modulated track on which a wobble modulation signal, obtained by modulating the wobble signal, is recorded.
The wobble modulation signal may be a wobble signal after having been phase modulated or a binary data of a predetermined length after having been subjected to binary phase shift keying (BPSK), where an autocorrelation R(xcfx84) of the wobble modulation signal has a maximum value where xcfx84=0 and is substantially 0 where xcfx84xe2x89xa00. The wobble modulation signal may be a signal having a white noise characteristic and a pseudo random (PR) sequence. Where the wobble modulation signal is processed by a finite impulse response (FIR) filter, where the equation describing the filtering characteristics of the FIR filter has the values of the bits of the wobble modulation signal as its coefficients, the frequency characteristic of the wobble modulation signal is substantially 0 in a DC area. The header region is positioned at the boundary region between sectors and comprises a plurality of portions displaced from the center of the wobbled track. The header information is recorded in the form of pre-pits, which are formed along the center of the wobbled track.
In another aspect, there is provided a method of detecting a header region from a recording medium including a wobbled track on which a wobble signal is recorded and the header region on which header information is recorded. The method comprises: detecting a wobble modulation signal from a wobble-modulated region on which the wobble modulation signal is recorded; demodulating the detected wobble modulation signal; outputting a header indicator signal based on an autocorrelation of the demodulated wobble modulation signal; and detecting the header region based on the header indicator signal.
The header region is positioned at the boundary region between sectors, and the wobble-modulated region is formed between the wobbled track and the header region. The wobble modulation signal, which is the wobble signal after having been phase modulated, is binary data of a predetermined length after having been subjected to binary phase shift keying (BPSK) and is a pseudo random (PR) signal. An autocorrelation R(xcfx84) of the wobble modulation signal has a maximum value where xcfx84=0 and is substantially 0 where xcfx84xe2x89xa00. The autocorrelation function R(xcfx84) provides a measure of how closely the signal matches a copy of the signal as the copy is shifted xcfx84 units in time. The frequency characteristic of a finite impulse response (FIR) filter, the equation describing the filtering characteristics of which has the values of the bits of a wobble modulation signal as its coefficients, is substantially 0 in a DC area. In the demodulating of the detected wobble modulation signal, the wobble modulation signal is demodulated based on a clock signal which is generated based on the wobble modulation signal. The outputting of the header indicator signal comprises: multiplying each node value, which is obtained by sequentially delaying binary data as a wobble modulation signal, by a corresponding bit of the binary data; and adding the multiplied node values.
In still another aspect, there is provided an apparatus for detecting a header region from a recording medium including a wobbled track on which a wobble signal is recorded and the header region on which header information is recorded. The apparatus for detecting a header region comprises: a clock signal generator which receives a wobble modulation signal which is detected from a wobble-modulated region and outputs a clock signal, a demodulator which receives and demodulates the wobble modulation signal based on the clock signal output from the clock signal generator, and a correlator which performs an autocorrelation on the demodulated wobble modulation signal from the demodulator and outputs a header indicator signal based on the result of the autocorrelation.
The wobble-modulated region is formed between the wobbled track and the header region, and the header region is positioned at the boundary region between sectors. The wobble modulation signal, which is the wobble signal after having been phase modulated, is binary data of a predetermined length after having been subjected to binary phase shift keying (BPSK) and is a pseudo random (PR) signal. An autocorrelation R(xcfx84) of the wobble modulation signal has a maximum value where xcfx84=0 and is substantially 0 where xcfx84xe2x89xa00. The correlator comprises: a finite impulse response (FIR) filter which multiples node values, which are obtained by sequentially delaying the wobble modulation signal, by corresponding bits of the wobble modulation signal, respectively, and adds all values obtained from the multiplications; and a header reader which compares the level of a signal output from the FIR filter with a predetermined reference level and outputs the header indicator signal for detecting the header region. The FIR filter comprises a delay unit which receives and sequentially delays the modulated wobble modulation signal, a multiplier which multiplies each delayed signal from the delay unit by a corresponding bit of the demodulated wobble modulation signal, and an adder which adds all the outputs of the multiplier. The frequency characteristic of the FIR filter with respect to the wobble modulation signal input thereto is substantially 0 in a DC area.